LIFE-SYSTEM OF DEVONIAN AGE— PLANTS. 329 



The Ferns were represented by several genera, such as Cyclopteris 

 and Neuropteris ; the Lycopods (club-mosses) not only by the Psilophy- 

 ton, which had been already introduced in the uppermost Silurian, but 

 also now by gigantic L&pidodendrids and Sigillarids, and the Equi- 

 setae by Calamites and Asterophyllites. The Conifers were represented 

 by the genus Protaxites, allied to the yew (Taxus). They are known 

 to be conifers by their concentric rings of growth and gymnospermous 

 tissue, i. e., the elliptic disk-like markings on the walls of the wood- 

 cells on longitudinal section (Figs. 389 and 390), and the entire absence 

 on cross-section of the visible pores so character- 

 istic of dycolytedonous Exogens (Fig. 391). 

 Some of these conifers have been found by Daw- 

 son eighteen inches, and one three feet, in diam- 

 eter. There have been fifty species of land- 

 plants of these various orders found by Daw- fig. 391.— Pine-wood, cross- 



,-■ r, • 4? at ci x- i t Section magnified. 



son m the Devonian 01 JNova Scotia alone. In 



Figs. 392-402 we give the most characteristic Devonian land-plants. 



General Remarks on Devonian Land-Plants. — We will not at present 

 discuss the affinities of these plants, and their relations to evolution, 

 because they are similar to those found in the coal, where they exist 

 in far greater variety and abundance, and the subject will be discussed 

 under that head. There are, however, some thoughts suggested by 

 the first appearance of highly-organized plants which ought not to be 

 omitted : 



1. The ringed structure of Devonian conifers shows that, at that 

 time, there was a growing season and a season of rest, and therefore, 

 probably, a warm and a cold season. In one trunk the number of rings 

 counted was 150, indicating a considerable age. 



2. "What were the precursors of this highly-organized forest vegeta- 

 tion? That there ivere precursors, from which these were derived, 

 there can be no doubt, for we have already found them in the Upper 

 Silurian ; but that the steps of evolution were just at this point some- 

 lohat rapid, seems also certain. It is impossible to account for this 

 comparatively sudden appearance of so highly-organized a vegetation 

 by evolution, unless we admit that there have been periods of rapid 

 evolution, as explained on page 302. When all the conditions are 

 favorable for a great advance, the advance takes place at once, i. e., 

 with great comparative rapidity. 



3. We have seen that the coal vegetation is to a large extent an- 

 ticipated in the Devonian. So, also, to some extent, were the condi- 

 tions necessary to the preservation of this vegetation and the formation 

 of coal. In the Devonian, for the first time, we find dark bands be- 

 tween the strata, impregnated with carbonaceous matter. We find, 

 also, thin seams of coal, with under-clays filled with ramifying rootlets, 



